Feline Masticatory Muscle Myositis – NAVLE Study Guide

Overview and Clinical Importance

Masticatory Muscle Myositis (MMM) is an immune-mediated inflammatory myopathy that targets the muscles of mastication. While extensively documented in dogs, MMM has been considered rare or questioned to exist in cats. However, recent case reports have confirmed that feline MMM does occur, presenting with clinical signs of restricted jaw mobility (trismus) and masticatory muscle atrophy. The disease involves autoantibodies directed against unique type 2M muscle fibers found exclusively in the masticatory muscles.

Feline masticatory muscles, like their canine counterparts, contain type 2M fibers with a unique myosin isoform not present in limb muscles. This makes them a specific target for autoimmune attack. Early recognition and treatment are critical for a favorable outcome, as chronic cases may develop irreversible fibrosis and permanent jaw dysfunction.

Anatomy of Masticatory Muscles

The masticatory muscles are responsible for jaw movement and include four paired muscles. All are innervated by the mandibular branch of the trigeminal nerve (CN V3), except for the caudal belly of the digastricus, which is innervated by the facial nerve (CN VII).